Posterous Groups is an attractive and easy-to-use group collaboration tool allowing users to keep up to date with groups of friends, family, or co-workers through email as normal, but have it stored and accessible via Posterous. (It's sort of like a friendlier variation of Google Groups.) Images, video, other embeds…

Earlier this year we reviewed Clutterpad, a group-focused task and project management tool packed with shared calendars, messaging, time tracking, and more. They've since tweaked their interface, increased usability, and added a time-saving to-do template feature for recurrent task sets.

Think of EtherCodes as EtherPad for developers. Featuring line numbers and syntax highlighting, it lets you code with a group, in a web browser, in realtime, without sacrificing some of the comforts of your favorite text editor.

KoHive is a virtual workspace you access through your web browser. It's easy to create multiple "hives" for different projects, share files, communicate in real time, and aggregate content from across the web.

Got an article to write with a fellow classmate? Need some feedback on a blog post you're putting together? Entri lets you write with a good editor, grab the link, then share it with friends to chime in.

Listiki is a crowdsourced list creation service. You create lists and others participate in adding to and ranking the contents of your lists. Best Windows applications, vampire movies, restaurants in Reno, worst CG movie—anything you can rank is fair game.

Microsoft rolled out its free Office Web Apps earlier this week, introducing a free, basic Office suite for the web. How does it compare to Google's own Docs offering? Here's a rundown of each webapp's strengths and weaknesses.

Real-time collaboration tool Google Docs is handy for simultaneously working on projects with multiple people, but it requires a Google account for all users. The new Google Docs Demo creates quick collaborative documents with a 24-hour shelf-life, no Google account necessary.

If you want to quickly and collaboratively edit documents with no fuss or burden on the other parties editing with you, Sync.in offers dead simple collaborative document editing with one-click sharing.

Google Wave now lets anyone with a Google account jump in and see what the early adopters have been squawking (and snarking) about. Head to wave.google.com now to get Waving, but read on for some beginner tips and use cases.

Windows only: Collaboration on projects is much easier than it used to be with services like Google Docs, but if you need some of the features in Office itself, free plug-in CircleDoc makes real-time collaboration possible in PowerPoint 2007.

Growing out of the shell that was cc:Betty, Threadbox aims to do the same kind of multi-recipient email organizing, but with a more business/client focus. To your email conversations, Threadbox attaches tasks, files, maps, and other collaboration data.

If you like Google Wave's real-time collaboration but not the interface or registration, check out TypeWith.me. It's a solid, simple, as-you-type document collaboration webapp with no sign-up required.

If you attend a lot of online or phone-based meetings, chances are you may love Ketchup, a snappy web-based meeting-notes manager that keeps track of agendas, attendees, action items, who said what, and more.

Web Server w/ PHP: If you're not too keen on hosting your team's projects on a 3rd party server—or pay the high fees associated with commercial project management tools—Collabtive is an open-source project management suite you can host yourself.